Vehicles sold in North America are required to adsorb refueling, diurnal, and running loss fuel vapors within a fuel vapor canister. Once the canister is loaded with vapors, engine intake vacuum may be used to draw fresh air through the canister, desorbing the fuel vapors to the engine intake where they may be combusted.
Activated carbon granules or pellets are commonly used to adsorb hydrocarbons within the fuel vapor canister. As the canister ages, carbon dust may break away from the granules, and may be drawn into the canister purge line during purge events. Buildup of carbon dust within the purge line may prevent complete closure of a canister purge valve, causing the valve to leak. A leaky purge valve results in engine vacuum being applied to the fuel system constantly, which may damage the fuel tank and other fuel system components, may result in unmetered fuel vapor being drawn into the engine, and may increase levels of undesired emissions.
Other attempts to address purge valve fouling include placing a carbon dust filter within the fuel vapor canister to prevent the egress of carbon dust into the purge line. One example approach is shown by Pearce et al. in U.S. Pat. No. 8,752,530. Therein, a filter is placed within the canister near the purge port. However, the inventors herein have recognized potential issues with such systems. As one example, the carbon dust filter may become clogged over time, reducing the effectiveness of purge routines. As such, the canister may become saturated with fuel vapor, increasing undesired emissions. Further, undesired emissions tests may be affected if engine intake vacuum is used to evacuate the fuel system via the canister purge port.
In one example, the issues described above may be addressed by a method for an engine wherein purge air is routed through a fuel vapor canister during a first condition such that desorbed fuel vapor traverses a canister purge port en route to an engine intake, and wherein purge air is routed through a fuel vapor canister during a second condition such that desorbed fuel vapor traverses a canister load port en route to the engine intake. Bypassing the canister purge port during a canister purge event allows for cleaning adsorbed fuel vapor from the canister even if flow through the canister purge port is restricted. In this way, vehicle emissions may be mitigated during conditions where a carbon dust filter at the canister load port is clogged.
As one example, a purge routing valve may be used to bypass the canister purge port by coupling the canister load port to a canister purge line if the canister purge port is restricted. Such a purge routing valve also allows for diagnostic testing to discern flow restrictions through the canister purge port. In this way, the life of the canister may be increased by merely replacing a clogged carbon dust filter rather than the entire canister.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.